Road-marking equipment generally includes a self-propelled vehicle which is driven by an operator over a surface while a stripe or line of marking material is applied to the surface. The vehicle carries the road-marking material and all of the equipment necessary to apply the material in a stripe to the road surface; for example, applicators, air compressors, supplemental engines, supplemental fuel supplies, and heat generator systems. Road-marking materials, including thermoplastic materials alkyd-based paint, chlorinated rubber-based paint, acrylic-based paint and paint containing water-soluble polymers require heating prior to their application to a road surface. Several types of heating systems have been used in the past, all with certain drawbacks.
One type of heating system utilizes a fired boiler which heats a heat exhange medium, such as an anti-freeze or oil mixture, which after heating by the boiler is transported to an indirect heat exchanger to transfer its heat to the road-marking material. This type of system suffers both maintenance and safety drawbacks. A flame source, fueled by a volitile substance such as propane gas, diesel fuel, fuel oil or kerosene, heats the boiler and presents a potential fire hazard, particularly since the vehicle carries other combustible substances such as flamable marking material, gasoline, or diesel fuel. This danger is further complicated by the thermostatically controlled electrical ignition system, typically used to control the start-up of the boiler. For example, if the burner fails to ignite properly, the boiler can become flooded with fuel so that when ignition does occur an explosion can occur. Total destruction of striping trucks have been reported due to boiler-related fires.
Another road-marking material heating system, developed primarily to alleviate the safety problems of boiler systems, is an indirect heating system wherein heat generated by the various motors on the vehicle is utilized to indirectly heat the road-marking material. These systems derive their heat from one or more sources, such as the engine-coolant, exhaust gasses, or hot compressed air. Examples of such systems are found in U.S. Pat. Nos. 3,092,325 and 4,190,205. While alleviating some of the safety problems of boiler systems, such systems generally do not produce enough heat to adequately heat road-marking material so that it can be applied at today's higher striping speeds.
A third type of heating system utilizes direct mechanical or friction heating of the marking material itself. Such a system is illustrated in U.S. Pat. No. 3,830,718. This system, however, also suffers numerous drawbacks such as high manufacturing cost, tendency to break down the chemical elements of the road-marking material, and incompatibility with WATERBORNE or acrylic-based paint.